The invention relates to an intrinsically safe electrically magnetically operated hydraulic valve for electro-hydraulically controlled underground mining installations such as especially advancing support frame controllers, with an actuator housing, which accepts the coil bodies, the armature, the magnetisable core, and the operating pins of at least two electro magnets and on the head end for the operating pins of each electro magnet has a cut out for the arrangement of an operating stroke adjuster, with a head plate which can be removed from the actuator casing, which is provided with a manual operating device for each operating pin and is fastened to the head end of the actuator housing with a head seal inserted between them, with a valve block which can be removed from the actuator housing, which accepts the hydraulic multi-way valves and with the interposition of a base seal is fastened to the base of the actuator housing, and with an electronics housing which has a connector socket for connection to an intrinsically safe current supply and which accepts the operating electronics for the electro magnets, which is fastened on the side of the actuator housing.
A previously proposed electrically magnetically operated hydraulic valve with an adjusting device in a head end cut out is described in DE-U-20104677 of the assignee. The adjusting device is accessible and user friendly when the head cover is removed and facilitates the sensitive adjustment of the operating pin. In the head cover are integrated manual operation devices for operating the electro magnets or multi-way control valves in emergency situations. In internal trials of this hydraulic valve it has been shown that the clearly structured assembly of this valve based on the arrangement of the parts of the electro magnets in the actuator housing, the hydraulic parts in a separate valve block and the functional parts for manual operation, as for example protective sleeves of elastic material in the head cover is especially favourable for maintenance purposes. A dust and moisture tight seal is obtained by comparatively large surfaced head and base seals and these seals are themselves simply exchangeable. The base seal effects a complete separation between the electrical side and the hydraulic side of the electrically magnetically operated hydraulic valve and forms a further improvement in electrically hydraulically operating devices as opposed to the known hydraulic valves.
Since the electrically magnetically operated hydraulic valves are destined for underground application, they must comply with all the construction and test conditions for fire-damp and explosion protection and especially must satisfy the intrinsic safety spark protection class. In the commercially available intrinsically safe electrically magnetically operated hydraulic valve of DE-A-4140233, which has neither a cut out at the head end nor an integrated lift adjuster, the intrinsically safe operating electronics is encapsulated within the electronics housing by means of a cast mass and the electronics case is fastened to the actuator housing by means of a screw connection, which is cast in with the cast mass. Exchange of the intrinsically safe operating electronics is in this hydraulic valve not provided since the exchange would lead to a loss of the intrinsic safety spark protection Classification.
It is the aim of the present invention to produce an improved, maintenance and operationally friendly intrinsically safe electrically magnetically operated hydraulic valve for underground applications.
Accordingly the present invention is directed to an intrinsically safe electrically magnetically operated hydraulic valve as described in the opening paragraph of the present specification, in which each head end cut out an electronic protective circuit for the associated coil bodies is arranged. Owing to the integration of an appropriate electronic protection circuit for each coil body in the actuator housing, the requirement is also satisfied that the electronics case with the operating electronics can be disassembled and exchanged without the test conditions for the spark protection intrinsic safety being impaired. Advantageously the actuator housing, the head plate, the electronics case and the valve block are separable in a modular fashion from each other and can be replaced. The encapsulation or casting of the fastening means for the electrics case is no longer necessary.
In a preferred embodiment the electronic protective circuit comprises at least one freewheeling diode. In an electromagnet connected to a direct current supply, on breaking the current, short term voltage peaks arise, owing to the large voltages induced by the breakdown of the magnetic field, whose polarity is reversed to the direct voltage applied to the coil body. Using a freewheeling diode, which takes on the load current as soon as its voltage becomes positive the energy in the magnetic field can be broken down. With a protective circuit employing a freewheeling diode insulation damage to the coil windings of the coil bodies and other problems brought about by the voltage peaks can be avoided, whereby the intrinsic safety of the magnetic valve itself remains provided even with an exchange of the operating electronics because of the integrated protection circuits in the actuator housing. Instead of the freewheeling diodes other suitable electronic components as for instance varistors can be provided in the protective circuit, although the use of freewheeling diodes forms the preferred embodiment. Advantageously protective circuit and the freewheeling diode are components of a circuit board arranged in the cut out, which preferably forms an electronics insert, positioned in the cut out by simple means and anchored there so as to be fixed against vibration.
In a preferred embodiment of the intrinsically safe electrically magnetically operated hydraulic valve foresees an adjustment device which comprises an adjustment disk positively engaging on the operating pin, which can be retained in its adjusted position by a means of retaining pin which can be retained in the actuator housing passing through a cut out in the edge zone of the adjusting disk, as is described in detail in DE-U-20104677, to which on this subject express reference is made and whose content is imported by reference into the present application.
To optimise the sealing function of the head seal and/or the base seal, both advantageously comprise sealing plates with shoulder like or lip like swellings. These swellings can not only improve the sealing function to the bordering surface between the housing parts when brought together but since they are pressed together in the assembled condition they also store a separating force which eases the separation of the two. Preferably the head seal and the base seal have an identical or mirror image profile of each other so that the construction prevents the maintenance personnel from using an incorrect sealing plate or positioning the sealing plate the wrong way around.
In preferred embodiment the operating electronics in the electronic casing have a circuit for reducing the maintaining current in the feed of the electro magnetics from an intrinsically safe DC supply. Advantageously the actuator housing comprises a ferro-magnetic material in order to obtain an increase of magnetic force for the same coil current owing to the additional ferro-magnetic mass and thus to be able to reduce the operating current. It is then preferable to provide the actuator housing with a coating which comprises plastics material such as especially a duroplast or a suitable polymer, in order to protect the actuator housing from external influences due to moisture and to prevent corrosion arising on the ferro-magnetic parts. Advantageously for the positioning of the valve block and/or the head plate on the actuator housing at least one centering pin is provided. For the modular construction and easy exchange of one of the housings, preferably the screwing together of the valve block with the actuator housing and the screwing together of the head plate with the actuator housing can be loosened independently of each other.